1. Field of the Invention
This invention relates to a Christmas lamp, and particularly to a lamp string with an open-circuit-proof structure.
2. Description of the Prior Art
In a conventional Christmas lamp string, a plurality of separate lamp strings is connected in series into a long lamp string; in the separate lamp string, a power-supply wire having a suitable length is used to connect between two lamp assemblies in series; the first lamp assembly and the last lamp assembly are connected with different length of two power-supply wires to a plug; then, the whole lamp assemblies and the power-supply wires are twisted into a separate lamp string.
Each lamp assembly in one lamp string includes a socket, a bulb receptacle, and a bulb. In order to facilitate removing or replacement of a bulb, the bulb is usually mounted in a bulb receptacle, and then the bulb receptacle is plugged into the rectangular cavity of a socket. The number of lamp assemblies and the resistance of each lamp assembly are designed in advance in accordance with the voltage and current values of a local area.
In order to prevent the power-supply wire from being overloaded, or from having a short-circuit to cause a danger, the socket of each lamp string must be furnished with a fuse wire; however, the fuse wire in the socket is not designed in accordance with the overload value of the lamp assembly.
Each bulb of every lamp assembly has a glass positioning bead welded around two parallel magnesium-plating filaments; the short section of two filaments at one end of the positioning bead is connected with a tungsten filament, while the other end of the positioning bead has two longer filaments pulled out of the bulb sealed; the magnesium-plating filaments are plugged into the center hole of the bulb receptacle, and then the two filaments are bent and attached along two planes on both sides of the bulb receptacle respectively; after the bulb receptacle is plugged into the center hole of the socket, the filaments on both sides of the bulb receptacle will be in contact with the contact copper plates of the power-supply wires respectively; in such a lamp string, if the tungsten filament of only one bulb is burned out or one bulb is lost, the whole lamp string will be turned off because of the circuit is opened.
In order to prevent the aforesaid open circuit from taking place, a fuse made of aluminum of 0.065 m/m is wound around the two filaments on the outer end of the positioning bead before the tungsten filament being mounted on the tail ends of the two filaments; the number of turns of the fuse wire is at least 2.5 turns so as to enable the aluminum fuse fastened in place. The purpose of furnishing the aluminum fuse is to prevent the lamp string from suffering an open circuit in case of the tungsten filament in a bulb being burned out, i.e., the low resistance fuse will maintain the two bulb filaments in a conduction state to keep the whole lamp string in lighting-up condition.
When one bulb in the lamp string is lost, a new bulb must be mounted therein; in case of no such bulb being available, the replacement has to be abandoned.
The prime object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which each lamp assembly in a lamp string has a center hole; the center is furnished with rectangular cavity for mounting a fuse assembly; the outer rectangular cavity in the center hole is used for mounting a bulb receptacle with a bulb; since the socket is furnished with a fuse assembly, the whole lamp string will always be maintained in lighting-up condition in case of the tungsten filament of a bulb in the lamp string being burned out, or one of the bulb receptacle of the socket being lost because of the power-supply circuit being maintained in conduction condition by means of the fuse assembly.
Another object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which the fuse assembly mounted in the center hole of the socket includes a fuse member and a fastening member; the fuse member has a positioning bead, which is used for fastening the two parallel magnesium-plating filaments in place; the short section of the two magnesium-plating filaments is wound with a fuse made of aluminum, while the longer section of the two magnesium-plating filaments extend the through slots of the fastening member; then, the tail ends thereof are bent and attached to the two planes respectively. The two bent magnesium-plating filaments of the fuse assembly are in contact with the contact copper plates respectively; in case of the bulb receptacle being lost or the tungsten filament of a bulb being burned out, the power supply of the lamp assembly can still maintained in conduction condition through the magnesium-plating filaments of the fuse assembly.
Still another object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which a rectangular cavity is furnished under a rectangular cavity to mount the bulb receptacle, and it is used for mounting a fuse assembly; such fuse assembly would not hinder the bulb receptacle to plug in place.
A further object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which a fuse assembly is mounted in the center hole of the socket; the tail ends of the two magnesium-plating filaments are mounted with tungsten filament directly without winding aluminum fuse wire around the two magnesium-plating filaments.
A still further object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which the center of the fastening member in the fuse assembly has a recess, under which two through slots are furnished on both sides thereof; the two through slots are used to have the two longer section of magnesium-plating filaments passed through; the tail ends of the magnesium-plating filaments are bent and attached to the planes respectively; the recess in the center thereof is used for mounting the positioning bead so as to prevent the fuse member from moving unintentionally as a result of shaking.
Yet another object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which the longer section of the two magnesium-plating filaments at one end of the positioning bead is wound with aluminum fuse wire of 0.065 m/m at least 2.5 turns; normally, the aluminum fuse wire would not hinder the current flowing in the tungsten filament of the bulb; in case of the tungsten filament of a bulb being burned out or a bulb receptacle being lost, the low resistance aluminum fuse wire will maintain the power supply in a closed circuit condition and the whole lamp string will still be in lighting up condition.
Yet still another object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which the fastening member of the fuse assembly is substantially a rectangular block to be plugged in a rectangular cavity of the socket; the magnesium-plating filaments on both sides thereof are in close contact with two contact copper plates respectively.
Yet a further object of the present invention is to provide a lamp string with an open-circuit-proof structure, in which the fastening member of the fuse assembly is a rectangular block, of which the lower part has a rod; both sides of the rod are designed to fit to the power wire groove; after the fuse assembly is plugged in place, the rod will fill in the power wire groove between the two power-supply wires so as to prevent rain water from flowing into the rectangular cavity of the socket.